We have recently developed a new radiologic method for quantifying the extent of coronary atherosclerotic lesions by computer-assisted cinevideodensitometric analysis of coronary arteriograms. We have validated the accuracy of this method for measuring relative stenosis in both phantom radiographic experiments and in histologic studies of coronary arterial dimensions in human postmortem hearts. The research proposed in this initial application is designed to 1) validate the accuracy of this approach for measuring absolute cross-sectional area of coronary atherosclerotic lesions form cineangiograms; 2) determine the degrees of coronary stenosis which result in the following manifestations of ischemia in patients with coronary artery disease: reduced regional myocardial blood flow measured at rest by intracoronary xenon-133 clearance; abnormal regional blood flow during pacing-induced myocardial ischemia; reduced thallium-201 uptake during exercise treadmill testing; and exercise-induced left ventricular dysfunction detected by radionuclide angiography; and 3) describe morphometric features of atherosclerotic plaques, analyzed by computer cinevideodensitometry which increase the likelihood of coronary occlusion; and 4) correlate plaque morphology with reocclusion of coronary arteries in patients with acute myocardial infarction treated with intracoronary streptokinase. Regional myocardial blood flow at rest and during rapid atrial pacing will be determined by the intracoronary xenon-133 clearance method; myocardial perfusion during exercise will be determined by thallium-201 exercise stress testing; and exercise-induced left ventricular dysfunction will be non-invasively assessed by radionuclide angiography. All computer facilities necessary are available in our laboratory, and no capital equipment expenses are requested in this application. The basic goals of the proposed research are 1) to provide clinicians with an accurate quantitative method for evaluating the severity of individual coronary atherosclerotic lesions in patients preoperatively and 2) to provide clinicians with objective information about the degrees of coronary stenotic lesions which reduce regional myocardial flow at rest and during exercise, induce myocardial ischemia during exercise, and enhance the likelihood of coronary thrombosis. This data will be useful to clinicians evaluating individual patients for coronary surgical revascularization.